The present invention relates to a laser system producing multiwavelength light and, more particularly, to a Brillouin/erbium-fiber laser system producing multiwavelengths with a dual spacing of 10 GHz and 20 GHz.
In wavelength division multiplexing optical communications, a Brillouin/erbium-fiber laser outputting multiwavelengths has been widely developed. However, it is not proper the Brillouin/erbium-fiber laser to be applied to actual optical communications because the spacing between the multiwavelengths to be outputted is so narrow compared to the 100 GHz wavelength spacing, which is currently used.
When high intensity light is incident on nonlinear optical materials, the first order Stokes wave is generated in the reverse direction by the interaction between the incident photons and acoustic phonons, which is so-called xe2x80x9cStimulated Brillouin Scatteringxe2x80x9d.
Brillouin gyroscopes using the Stimulated Brillouin Scattering in optical fibers have been studied and, moreover, there are many researchers on the Brillouin/erbium-fiber laser, Brillouin optical fiber interferometers and Brillouin optical fiber laser interferometers.
One of notable paper is xe2x80x9cBrillouin/erbium fiber laser,xe2x80x9d by G. J. Cowle, et al., which is published in xe2x80x9cIEEE J. Lightwave Technol.xe2x80x9d In this paper, Brillouin/erbium-fiber laser outputting 10 GHz spacing unidirectional multiwavelength waves has been presented, in which optical signals, resonating unidirectionally in a ring-type laser cavity, feed back in the opposite direction thereto.
Further, in the paper of xe2x80x9cMultiwavelength operation of Brillouin/erbium-fiber lasers with injection-locked seedingxe2x80x9d by G. J. Cowle, et al., another Brillouin/Erbium optical fiber laser structure of bidirectional multiwavelength has been proposed in a spacing of 20 GHz, by using the ring-type laser structure. However, only 20 GHz spacing multiwavelength waves can be outputted.
In xe2x80x9cGeneration of multiorder Stokes and anti-Stokes lines in Brillouin/Erbium-fiber laser with Sagnac loop mirror,xe2x80x9d xe2x80x9cOptics Letters,xe2x80x9d 1988, Vol. 23, No. 21, instead of the ring-type laser structure, a Brillouin/erbium-fiber laser structure of the Sagnac resonator structure is proposed, but such an optical fiber laser obtains 10 GHz spacing multiwavelength outputs only.
As stated above, the conventional optical fiber laser can obtain multiwavelength optical outputs having only one spacing of 10 GHz or 20 GHz. However, an optical fiber laser capable of obtaining multiwavelenths of a dual spacing of 10 GHz and 20 GHz has not been presented to date.
Moreover, the proposed fiber laser may be used as a sensor. Namely, if the fiber laser capable of providing the multiwavelength output of a dual spacing is employed, it may be used as an optical fiber sensor. The variation of physical objects, such as temperature, pressure, current, magnetic field, and so on, can be used by measuring the relative variation of light intensity of 10 GHz and 20 GHz spacing signals.
It is, therefore, an object of the present invention to provide a Brillouin/erbium-fiber laser system producing multiwavelengths with a dual spacing of 10 GHz and 20 GHz.
It is another object of the present invention to provide a laser sensor using Brillouin/erbium-fiber laser generating multiwavelengths of a dual spacing.
In accordance with an aspect of the invention, there is provided an optical fiber laser system comprising: a Sagnac reflector generating even- and odd-order Stokes waves by launching input lights; a first means forming a first resonator with the Sagnac reflector, wherein the first means is coupled to a first directional coupler in the Sagnac reflector; a second means forming a second resonator with the Sagnac reflector, wherein the second means is coupled to the first directional coupler in the Sagnac reflector; and a third means for inputting Brillouin pump light into one of the first and second means, whereby the optical fiber laser system outputs multiwavelengths with a dual spacing.
The first means outputs even-order Brillouin Stokes waves and wherein the second means outputs odd-order Brillouin Stokes waves. The first means includes a second directional coupler coupled to the first directional coupler in the Sagnac reflector, transferring the Brillouin pump light to the Sagnac reflector; a first light amplifier coupled to the second directional coupler; a first wavelength division multiplexer coupled to the first light amplifier; and a third directional coupler coupled to the first wavelength division multiplexer for detecting an output of light. Also, the second means includes: a second light amplifier coupled to the first directional coupler in the Sagnac reflector; a second wavelength division multiplexer coupled to the second light amplifier; and a fourth directional coupler coupled to the wavelength division multiplexer for detecting an output of light.
Further, the first and second light amplifiers are Erbium Doped Fibers and the optical fiber laser system further comprises a fifth directional coupler coupled to the third and fourth directional coupler for receiving a pump light to achieve reverse of density of the Erbium Doped Fibers.
In the multiwavelength Brillouin/erbium-fiber laser according to the present invention, an optical fiber Sagnac reflector receives the Brillouin/erbium scattering pumped light from a single wavelength of an optical fiber laser and generates two kinds of multiwavelengths which are different from each other in their spacing. According to the multiwavelength Brillouin/erbium-fiber laser of the present invention, a directional coupler of the Sagnac reflector having a stimulated Brillouin/erbium scattering medium is coupled to the first and second optical fiber mirrors so that the coupling of the Sagnac reflector to the first optical fiber mirror and the coupling of the Sagnac reflector to the second optical fiber mirror respectively implement first and second laser resonators.
The Sagnac reflector, which is shared with the first and second laser resonators, includes an optical fiber (Brillouin/erbium scattering medium) of a few kilometers and a polarization controller for controlling birefringence. Even- and odd-order lights, which are different from each other in Brillouin scattering characteristics, of continuously oscillated multiwavelength Brillouin laser lights may be resonated in each laser resonator under the control of the polarization controller in the Sagnac reflector. Accordingly, the multiwavelengths are output in 10 GHz and 20 GHz spacing.